Power abhors a vacuum, and in the absence of strong U.S. leadership on Syria, Russia and Iran have been more than happy to move in. It's a measure of just how much they've come to dominate the conflict that they'll be the only major foreign powers at the summit. The White House has largely washed its hands of Syria. But with Iran entrenched in Damascus, and the Islamic State biding its time in the far countryside, it's likely only a matter of time before our hands are dirtied again. When that happens we'll likely look at these negotiations as a lost opportunity.